| Rice is one of the most important crop in China, but also one crop tends to be infested by many kinds of pests. The damage of rice pests has increased considerably since 1990's, with the changes of atmosphere temperature of the globe, rice cultivation system and the extension of hybrid varieties. An attractive alternative strategy for protection against the rice pest infestation is to produce insecticidal proteins by the rice plant itself through genetic engineering. Synchronously, potential ecological risk of insect-resistant transgenic rice released to environment has become a public concern. In this paper, we reported the results on the evaluation of transgenic rice lines expressing CrylAc and CpTI against lepidopterous pests and resistant risk of target pest to CrylAc toxin, and developed the resistance management strategy. The results are as follows.1. Datached leaf and stem bioassay, open field test and cage test were conducted to evaluate the control efficacy of transgenic rice lines (ⅡYouKF6 and KF6), expressing CrylAc and CpTI, against lepidopterous pests, Cnaphalocrocis medinalis, Chilo suppressalis and Sesamia inferens. The results showed that the percentages of plants with folded leaves and deadhearts/whiteheads and percentages of folded leaves and deadhearts/whiteheads in transgenic lines were significantly lower than those in control lines with and without chemical pesticides, showing high control efficacy against C. medinalis and C. suppressalis during the whole growing stages.2. Datached leaf and stem bioassay, open field test and cage test showed that control efficacy of transgenic rice lines against S. inferens differed significantly among different developmental stages. During seedling, tillering and jointing stages, the transgenic rice lines exhibited highly toxin and lethal effect to S. inferens. However, the transgenic rice lines during booting and grouting stages could not show obviously lethal effect to S. inferens, though they could significantly restrain the development and survival of S. inferens. So it considered that the transgenic rice lines reached the high dose to S. inferens in early developmental stages, but not in late stages.3. The influences of transformed crylAc and CpTI genes rice on biology of target pests were tested. The results indicated that the pupal weight of C. suppressalis and S. inferens feeding on transgenic rice lines was significantly lower than that on control rice lines. However, there was no significant difference in female adult fecundity between control and transgenic treatments, indicating that pupal weight significantly decreased after continuously feeding on transgenic rice lines but there was no significant effect on fecundity of C. suppressalis and S. inferens.4. Adult female moths of C. suppressalis were collected from light-traps to ascertain population variation in susceptibility of C. suppressalis to Bt toxins. Each female producing enough fertile eggs for bioassay was used as the parent of an isofemale line. Of 1,100 females collected, 395 isofemale lines producing enough offspring were screened on a diet assay treated with CrylAc. The results showed that 51.7% of isofemale lines were differentiated as highly susceptible, 23.0% as moderately susceptible, 23.8% with low susceptibility and only 1.5% as non-susceptible with survival rate>70% and similar development as on non-Bt control diet. The results indicated significant variation in susceptibility to CrylAc in C. suppressalis population, which should be considered for insect resistance management of Bt rice in the future.5. Flight ability of C. suppressalis and S. inferens in different ages was measured in the laboratory with computer-linked flight mills. Both C. suppressalis and S. inferens exhibited high flight capacity in the second day of emergence. Compared to C. suppressalis, the S. inferens showed higher flight capacity. Therefore, S. inferens has more flexible capacity to use the natural refuge to delay its resistance evolution to Bt toxin, than C. suppressalis.6. Dispersal ability of larvae of S. inferens in rice at tillering and booting stages was tested with the method of artificial infestation and field investigation. The larvae of S. inferens showed extensive movement among plants in plots of transplanted rice, during the course of larval development. The larvae dispersaled within the released hill on days 1～7, and began to move to the other plants colsest to the released hill on days 8 after infestation. During the process of test, the longest dispersal distances of S. inferens on tillering and booting developmental stages of rice were all 120 cm, and the longest mean distances in dispersal were 62.29 cm and 51.02 cm, respectively. Compared to that on booting stage, the dispersal rate and distances of S. inferens on tillering stage of rice was significantly higher. If the planting measures of seed mixtures or refugia within Bt field will be adopted as the resistance management strategy, the larval will move between Bt field and non-Bt field and consume tissue from both Bt and non-Bt plants. This behavior will reduce the cumulative dose of toxin ingested and accelerate the evolution of resistance. Therefore, external refuge could effectively delay the resistance evolution of S. inferens. 7. The model parameters were obtained based on the results of the 2nd, 3rd and 4th chapters and regressive models about the optimal spatial configuration of refuges were established. Our simulative results showed that the optimal percentages of refuge with and without chemical control for C. medinalis were 2% and 7%, respectively. The percentages of refuges without insecticide sprays for C. suppressalis increased with the increase of the distances between refuge and Bt rice field. When the distances between refuges and Bt rice field were<1 km, 1 km～3 km and>3 km, the optimal percentages of refuges were 10%, 12% and 15%, respectively. |
PDF Full Text Request